Preparation of dithiobiuret



June 26,'1951 1|.. c. LAN, JR., ErAL u 2,557,980

' PREPARATION oF DITHIOBIURET Filed March 15, 1949 3 Sheets-Sheet 1 fy" fo/rH/os/z/Pfr C14/f5 l FM nu? BY @du L'. HMM- V ATTORNEY June 26, 1951 c. LANE,.JR., ETAL PREPARATION oF DITHIOBIURET 3 Sheets-Sheet 2 Filed March 15, 1949 TEMPI/P4 ra/Pf INVENTORS June 26, 1951 L. c. LANE, JR., ETAL PREPARATIoN oF DITHIOBIURET Filed March 15, 1949 3 Sheets-Sheet 3 Has C/PUEBFI? INVENToRs L Au /f C. 7A/f, JR., fwn/awp@ W. #4MM 70N BY @lahm/J L.v MW

ATTORNEY Patented June 26, 1951 UNITED fs rArr.:

''I'EN T OF F IC E PREPARATION 0F DITHIOBIURET -Leslie C. Lane, .Jr., Stamford, and Richard W.

Hamilton, v.Ner.vvalk, Conn., assignors to Ameri- .can Cyanamid Company, `New York, N. Y., a

corporation of Maine Application March l5, 1949, Serial N0. 81,463 19 Claims (Cl. 260-552) to prepare dithiobiuret Aina manner not vrequiring the useof pressure apparatus.

The invention also contemplates .the production Yof dithiobiuret `from afsolution of Vcalcium-dicyanimide :that also contains calcium-chloride as a by-prcduct .in the preparation of said calcium dicyanimide, and it is-one object:of this inven- -tion to proceed .from calcium cyanamide and cyanogen-chloride, with the addition of hydrogen sulfide atan intermediate stage, finally 'todithiobiuret, without the use .of solid calcium. `dicyani- .mide at any `stage :of the process.

Additional-objects Will-appear-from the description yof the invention hereinafter.

Figure Vl is ow chart `showing one embodiment of l.the invention.

Figure 2 .represents the solubility curve of -dithiobiuret in water.

Ias

.It has `been .found that -dithiobiuret may :'be

obtained Rby warming Yan vaqueous solution `or suspension `of a metal ydicyaniinide k-vvith hydrogen suliide. YC-yanothiourea iirst forms and reacts with more hydrogen sulfide -to yield VVdithiobiuret. -Unreactedcyanothiourea may .be separated -f-rom the .iinal product as described hereinafter.

The following .reactions -are postulated:

CN-N-CN narily insoluble .in Water. In the present reaction, however, no metallic-sulfide or'other `metallic Icompound precipitates, and `it is 4assumed i.

that if Casisiormed, .it is retained in solution as -an `unidentiiied complex. ln any event, .the metallic part .of .the Ydicyanirnide .remains insolutionduring the subsequent .working .up ,of the Yre- .action mass and does not interfere Vwith the ref covery of either yditliiobiuret or .cyanothiourea 4A stock solution of .calcium .dicyanimide `suitable as a starting material 'for the addition of hydrogen sulfide in some of the examples that follow may be prepared `by .slurrying crude cal- 2 cium cyanamide with-cyanogenlchloride.in water, filtering, and'using .the thus-formed solution foi calcium ydicyanimide and Vcalcium chloride as the reaction menstruum. This is probably the most economical method of conducting the process.

PREPARATION OF :STOCK *.SOLUTON I'OF TCAIOIUM .DIOYANIMIDE vReactants I Molar .Ratio .Cyanogenchloridc l. 0 Crude calcium cyanamide (58%) 1.0 Water 27. 8

The cyanogen chloride is carefully 'added yto the 'agitated aqueous slurry of crude calcium cyanami'de at al-rate of abouti mollper 05"hour. The temperature range 'is substantially'2830 1C. and 'the cyanogen chloride is Aabsorbed readily` As soon as exothe'rm'ic 'tendencies stop, 'the lreaction mixture is neutralized 'with dilute hydrochloric acid. The insoluble impurities are 'removed and fa clear, slightly 'yellow zi'lltrate is obtained, which 'contains mainly calcium Vdicyanimide and calcium chloride. The calcium chloride does notinterfere with subsequent 'production of dithiobiuret.

"Various modifications ofth'einvention are Vmore fully described in 'th'e .following examples.

Eixample 1 OPEN FLA'sK yMETHOD n(iwi/ing to the high `rsolubility :of 'calcium-'dicyanimide in water (up to 47% at 25 CJ) fa1wide range of concentrationsis available.

A 10.3 aqueous solution containing 47.8 grams of calcium dicyanimide (both gures were arbitrary) -Was placed in 'a yone-'liter 'three-neck flask equipped with ra .stirrer, v'redux condenser, thermometen and sintered Aglass disc vgasiiier 'for hy- .drogen sulde addition. The hydrogen sulde was passed `rapidly into -the vigorously 'stirred `solution -for three .-hours, during which time 'the 'solution was held at a temperature of 95 C. No `attempt e.was 4made vto control vthe -pI-Lof the solution, which was about-8.4 initially and which obtained by acidifying the solution with hydrochloric acid or the like to a pI-I of about 2-3. (Acidication may be carried out either before or after chilling.) The solution was allowed to stand for about half an hour to permit the growth of 1iarger crystals and the crude precipitate, comprising essentially dithiobiuret and cyanothiourea, was iiltered off. The filter cake was dissolved in a minimum amount of boiling water to convert any cyanothiourea present to an insoluble substance ci unknown composition, diatomaceous earth was added as a clarification agent, and the solution was filtered and cooled slowly to room temperature, whereupon crystals of dithiobiuret formed. These crystals were nltered off, dried, and weighed. The yield was 32.8 grams, 44% of theoretical.

The time of reaction is critical, for if a reaction conducted at 95 C. is stopped before 11/2 hours, little or no dithiobiuret is obtained. I-Iowever, excellent yields are obtained after a reaction of two hours, and the optimum yields are obtained at about three hours. From that point on, the yields tend to decrease, and after iive hours the yields become rather low.

The temperature of reaction is also critical. Below 65 C., unless the reaction is continued for an unusually long period, the yield of dithiobiuret is quite low, increasing as the temperature approaches 100 C.

In some instances enough cyanothiourea may remain unconverted to make its recovery worth while. In this case, after the reaction is stopped, it is chilled to -l0 C., the pI-I adjusted to about by addition of sodium hydroxide, ammonia, or the like, if it is not already about 10, (cyanothiourea being soluble in cold alkaline solution and dithiobiuret relatively insoluble), the resulting precipitate of dithiobiuret is removed, the solution is acidied with hydrochloric acid or the like to a pH of 2-3 to cause cyanothiourea to precipitate, and the same is recovered.

In an alternate method the reaction is stopped, the solution chilled to 5-10 C. and acidied to a pI-I of 2-3 to precipitate both dithiobiuret and cyancthiourea; the precipitate is recovered and slurried in a neutral solution or one made alkaline by the addition of sodium hydroxide, ammonia, or the like, up to a pI-I of about 10 to redissolve cyanothiourea, undissolved dithiobiuret is removed, the solution is acidied to a pH of about 2-3 to precipitate cyanothiourea, and the same is recovered.

Example 2 FORMATION oF HmnoonN sULFinn iN si'io Instead of adding hydrogen sulfide to the reaction mass through a sintered glass gasifier, it may be added to the reaction mass by formation in situ. The following procedure is typical of various processes that may be used when hydrogenV sulfide is to be formed in solution. The calcium dicyanimide solution is placed in a flask equipped with a stirrer, reux condenser, thermometer, and two dropping funnels with stems reaching nearly to the bottom of the vessel. As the solution is heated and stirred, a 40% aqueous solution of sodium sulztliydrate, and concentrated hydrochloric acid are added slowly through their respective dropping funnels at a rate such that the pH remains as nearly as possible at 8-9. An excess of sodium sulfhyclrate is preferred, in which event some of the hydrogen sulde generated in situ is not absorbed, but will escape from the reaction vessel via the reux condenser. ISO

lation of the product is carried out as in the preceding example. Slightly better yields are obtained by this method of adding hydrogen suliide.

In a specific example, 47.8 grams of calcium dicyanimide in 470 grams of solution were prepared and placed in the flask as above noted, and then 102.2 grams of sodium sulfhydrate were added simultaneously with the addition of 185 grams of 37% hydrochloric acid. The reactants were maintained at a temperature of C. for about three hours, and the pH was maintained Within the range '1.9 (initial) 8.7 (final), giving a yield of 47.7 grams of dithiobiuret, 64% of theoretical. While the pH range may vary, the range of about 8-9 is preferred, and this range may be maintained by varying the addition of the sodium sulfhydrate and hydrogen sulde.

The method of using hydrogen sulfide formed in situ has the commercial advantage of being considerably cheaper than using hydrogen sulfide from a tank supply.

Example 3 METHOD USING REACTION TOWER Another method of preparing dithiobiuret according to the principle of this invention is shown diagrammatically in Fig. 3, and is more fully described as follows:

An aqueous solution of calcium dicyanimide is run into reaction vessel I, which is heated by steam jacket 2 or the like. A reaction tower 3 packed with Berl rings or similar contact surface materials and heated by steam jacket 4 or the like is connected to vessel l from above. 'Io the bottom of the vessel is attached a lagged line 5 to permit the continuous pumping of the solution from the vessel into the reaction tower. Simultaneously hydrogen sullde is passed into the vessel, through duct S, and it rises into the reaction tower and reacts with the calcium dicyanimide solution flowing down through the tower packing. The I-IzS pressure release valve 1 of any well-known design is adjusted to release I-IzS into HzS scrubber 8 at a pressure slightly over atmospheric (indicating substantial completion of the reaction), in which event, in a batch-wise operation, the reaction mass is removed from the vessel through duct 9. Using this embodiment, 119 parts by weight of calcium dicyanimide were dis solved in '750 parts by Weight of water, and the solution was run into a vessel connected to a reaction tower as above described, and continuously pumped from the vessel into the tower, while simultaneously an excess of hydrogen sulfide was forced into the Vessel and permitted to rise through the tower. The reaction was continued for about 1% hours, during which period the system was maintained at a temperature of approximately 93-95 C. No attempt was made to control the pH of the system, which was 8.4 in the beginning and 10.2 at the end of the period. The yield of dithiobiuret was 98 grams, 53% of theoretical. Some hydrogen sulde was consumed in the production of various impurities and in reacting with side products. The tower process is run continuously by pumping oi the product continuously While pumping hydrogen sulde and metal dicyanimide continuously into the vessel I. The rates of addition of reactants and removal of product are preferably adjusted to maintain a slightly superatmospheric pressure of hydrogen sulfide in the system.

. In the packed-tower batch method of prepar- 15 ing dithiobiuret, the time of reaction is critical,

' assenso 'a reactionperiod of one hour being insufficient der-these conditions a yield of only 25% was obtained.

The proportions of the absorption column may vary widely, due regard being given to eiilcient absorptiton of hydrogen sulde. In this and in the preceding methods, it is preferred that the hydrogen `suliide be in contact with the reaction mass during the entire heating period. If the addition of hydrogen sulde is stopped and heating isfcon-tinued, the yield of dithiobiuret drops.

Aof the periodic table a-s shown on pp. 54-55,

Langes Handbook of Chemistry, thv ed., are typical of the dicyanimides available for the process of the invention.

Ammonium dicyanimide, prepared from calcium dicyanimide and ammonium sulfate, Was

reacted with hydrogen sullde in an open flask at 95 C. for three hours.

biuret was obtained.

Magnesium dicyanimide, prepared from calcium dicyanimide and magnesium sulfate, was re- A 40% yield of dithio- .acted with the theoretical amount of hydrogen sulde in an autoclave at 80 C'. for forty-five minutes. A 60% yield of dithiobiuret was obtained.

Sodium or potassium dicyanimide was also used in analogous reactions, with good'yields of dithiobiuret.

The dicyanimides above discussed are water soluble, but this property is not a requisite for the preparation of dithiobiuret. For example, zinc dicyanimide, which is relatively insoluble, was prepared from calcium dicyanimide and zinc chloride and was slurried in water made alkaline with 5% by weight of ammonia, based on the weight of the zinc dicyanimide used. Slightly less than the theoretical amount of hydrogen sulde was added, and the mixture was heated to 80 C. for forty-ve minutes. A 60% yield of dithiobiuret was obtained. While a small amount of dithiobiuret may be obtained without making the solution alkaline, the yield is increased if the pI-I is in excess of '7.

Example 5 METHOD USING AUTOCLAVE While it is a particular advantage of the present process that an autoclave is not required for the preparation of dithiobiuret, the best yields are obtained under superatmospheric pressure. A 10.3% solution of calcium dicyanimide containing 20.6 grams of calcium dicyanimide was 6 `placed in a S10-cc. autoclave, to lwhich was attached a smally transfer bomb containing 12.2 grams of hydrogen sulfide, the theoretical amount. The hydrogen su'lde Was forced from the transfer bomb into the autoclave by the applicationoi heat, the valves of the transfer bomb and the autoclave were closed, and the transfer bomb was disconnected. The autoclave and its contents were heated to about C. with rocking until the hydrogen sulfide was completely absorbed, as indicated by a pressure gauge reading of zero, which in this case required forty minutes. The highest pressure recorded was 570 p. s. i. The autoclave was then cooled rapidly, vented andl the contents removed. Dithiobiuret was isolated as in the preceding examples, the yield being 29.2 grams, or 90.7%. Yields of the same order may be obtained by reducing the temperature a little and increasing the pressure considerably. Thus, at '75 C. and 900 pounds per square inch, a yield of 89% was obtained.

For the autoclave method, the temperature and pressure cited in the preceding paragraph areY approximately optimum. For example, if the same temperature is used but with a lower pressure, in the range of 280 lli/sq. in., the yield drops to 75%. Similarly, if the pressure is maintained at about 500 p. s. i. but the temperature is decreased to about 65 C., the yield is decreased, 66.1% being typical. Two additional examples showing variations from the temperatures and pressures above given are as follows: When a high temperature of C. was used with a pressure of 300 p. s. i., a 23.3% yield was obtained. At a temperature of 11.0 C. and a pressure of 50 p. s. i., i. e., in addition to atmospheric pressure, a yield of 38.2% was obtained.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not to be limited thereto but is to be construed broadlyand restricted solely by the scope of the appended claims.

We claim:

1. The method comprising heating a metal dicyanimide, water, and hydrogen sulfide at a temperature of at least 55 C., at a pH in excess of 7 but not exceeding about 10.2 whereby a reaction mass comprising dithiobiuret is formed.

2. The method according to claim l in which the metal is a member of group Il-A of the periodic table.

3. The method according to claim l in which the dicyanimide is calcium dicyanimide.

l. The method according to claim l in which the dicyanimide is sodium dicyanimide.

5. The method according to claim 1 in which the dicyanimide is ammonium dicyanimide.

6. The method comprising heating a metal dicyanimide, water, and hydrogen sulde to a temperature of at least 551 C., at a pI-I in excess of 7 but not exceeding about 10.2 whereby a reaction mass comprising substantially dithiobiuret and cyanothicurea is formed, and recovering the thus-formed dithiobiuret and cyancthiourea.

7. The method according to claim 6 in which the metal is a member of group II-A of the periodic table.

8. The method according to claim 6 in which the dicyanimide is calcium dicyanimide.

9. The method according to claim 6 in which the dicyanimide is sodium dicyanimide.

l0. The method according to claim 6 in which the dicyanimide is ammonium dicyanimide.

ll. The method comprising heating a metal dicyanimide, water, and hydrogen sulde at a temperature of at least 55 C., at a pH in excess of 7 but not exceeding about 10.2 whereby dithiobiuret and cyanothiourea are formed, cooling the reaction mass to precipitate dithiobiuret and cyanothiourea, and isolating the thusformed dithiobiuret and cyanothiourea from the reaction mass and from each other.

12. The method comprising heating a metal dicyanimide, water, and hydrogen suliide at a temperature of at least 55 C., at a pI-I in excess of '7 but not exceeding about 10.2 whereby dithiobiuret and cyanothiourea are formed, cooling the reaction mass to a temperature below about C., acidifying the reaction mass to a pH within the range of about 2 to about 3, whereby dithiobiuret and cyanothiourea are precipitated from solution, and isolating the last two products from the reaction mass and from each other.

13. The method comprising heating a metal dicyanimide, water, and hydrogen sulcle at a temperature of at least 55 C., at a pH in excess of 7 but not exceeding about 10.2 whereby dithiobiuret and cyanothiourea are formed, aciditying the reaction mass to a pH within the range of about 2 to about 3, cooling the reaction mass to a temperature below about 5 C., whereby dithiobiuret and cyanothiourea are precipitated from solution, and isolating the thus-formed dithiobiuret and cyanothiourea from the reaction mass and from each other.

14. The method of separating dithiobiuret from a mixture comprising dithiobiuret and cyanothiourea which includes the steps of subjecting said mixture to the action of waterA at a temperature of at least 95 C., whereby dithiobiuret is dissolved but cyanothiourea is converted into an insoluble substance, removing said insoluble substance from solution, cooling the solution to vprecipitate dithiobiuret, and removing the thusdicyanimide, water, and hydrogen sulilde in a closed reaction zone, whereby dithiobiuret is formed, and recovering the thus-formed dithio biuret.

17. The method comprising heating calcium dicyanimide, water, and hydrogen sulfide at a temperature of at least 60 C., under superatmospheric pressure, for about 40 minutes.

18. The method comprising subjecting an aqueous solution of a metal dicyanimide to the action of hydrogen sulfide in a liquid-vapor contact tower at a temperature of at least C. and recycling the solution at a pH in excess of 7 but not exceeding about 10.2 until the dicyanimide is substantially converted to dithiobiuret,

and recovering the thus-formed dithiobiuret.

19. The method 'of preparing dithiobiuret which comprises forming an aqueous slurry of crude calcium cyanamide, mixing said slurry with cyanogen chloride, maintaining the reaction mixture at a temperature between 0-50 C. until calcium dioyanimide is formed, separating insoluble impurities from the reaction mass, adjusting the pH of the remaining solution to 8-10, adding hydrogen sulde to form dithiobiuret, cooling the solution to a temperature below about 10 C., whereby dithiobiuret is precipitated, and` recovering the thus-precipitated dithiobiuret.

LESLIE C. LANE, JR.

RICHARD W. HAMILTON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,371,112 Sperry Mar. 6, 1945 2,410,862 Bousquet et al Nov. 12, 1946 OTHER. REFERENCES Wunderlich, Bern deut. Chem., vol. 19 (1886), p. 453 to 454.

Fromm, Ben deut. Chem, vol. 55 (1922), p. 808.

Short, Chem. News, vol, 126 (1923), pp. 100 to 101.

Franklin, Nitrogen System of Compounds, (1935), pps. 100, 122 to 123. 

1. THE METHOD COMPRISING HEATING A METAL DICYANIMIDE, WATER, AND HYDROGEN SULFIDE AT A TEMPERATURE OF AT LEAST 55* C., AT A PH IN EXCESS OF 7 BUT NOT EXCEEDING ABOUT 10.2 WHEREBY A REACTION MASS COMPRISING DITHIOBIURET IS FORMED. 